1. Field of the Invention
The present invention relates to a method for manufacturing a copper alloy and a copper alloy.
2. Description of the Related Art
Heretofore, since a Cu—Ni—Sn-based copper alloy is formed of relatively inexpensive metal elements and has a high mechanical strength, this copper alloy has been used as a rolled material of a practical alloy. In addition, a Cu—Ni—Sn-based copper alloy has been known as a spinodal decomposition type age-hardening alloy and has also been known as a copper alloy having an excellent heat resistance, that is, excellent stress relaxation characteristics at a high temperature, such as 200° C.
As a method for manufacturing a Cu—Ni—Sn-based copper alloy, for example, a method has been proposed in which, for example, a heat treatment in a temperature range of 600° C. to 770° C., an inter-aging processing at a processing rate of 0% to 60%, and a heat treatment in a temperature range of 350° C. to 500° C. for 3 to 300 minutes are sequentially performed (see Patent Literatures 1 and 2). It is disclosed that, in this method, unlike a heat treatment method performed from a single phase region at approximately 800° C. or more, a heat treatment is preformed from a temperature region of 600° C. to 770° C. at which two phases are in an equilibrium state, the structure is formed so that the two phases are uniformly dispersed in the matrix under room temperature conditions, and as a result, fatigue characteristics are improved. In addition, by an aging treatment performed at 350° C. to 500° C., the fatigue characteristics are further improved. Furthermore, a method performing a solution treatment at 800° C. or more prior to the heat treatment performed in a temperature range of 600° C. to 770° C. disclosed in Patent Literatures 1 and 2 has also been proposed (see Patent Literatures 3 and 4). It is disclosed that, in this method, since a processed structure present in an alloy can be completely eliminated by a heat treatment performed at 800° C. or more in a single phase region, besides the improvement in fatigue characteristics, the moldability and the stress relaxation characteristics can also be improved. In addition, another method has been proposed in which, after a solution treatment and a cold rolling treatment are performed on a Cu—Ni—Sn-based copper alloy in this order, a heat treatment is performed at a temperature of 250° C. to 500° C. for 1 hour or more, and continuous annealing is then performed at a temperature of 300° C. to 600° C. for 1 to 20 minutes (see Patent Literature 5). It is disclosed that, by this method, a flat mill-hardened material can be efficiently obtained.